1. Field of the Invention
The invention relates in general to solid deposition modeling, and in particular to a post processing technique to remove a non-curable phase change support material from a three-dimensional object formed from a curable phase change build material.
2. Description of the Prior Art
Recently, several new technologies have been developed for the rapid creation of models, prototypes, and parts for limited run manufacturing. These new technologies are generally called Solid Freeform Fabrication techniques, and are herein referred to as “SFF”. Some SFF techniques include stereolithography, selective deposition modeling, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, and the like. Generally in SFF techniques, complex parts are produced from a modeling material in an additive fashion as opposed to conventional fabrication techniques, which are generally subtractive in nature. For example, in most conventional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to targeted locations, layer by layer, in order to build a complex part. SFF technologies typically utilize a computer graphic representation of a part and a supply of a building material to fabricate the part in successive layers. SFF technologies have many advantages over conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts and can produce limited numbers of parts in rapid manufacturing processes. They also eliminate the need for complex tooling and machining associated with conventional subtractive manufacturing methods, including the need to create molds for custom applications. In addition, customized objects can be directly produced from computer graphic data in SFF techniques.
Generally, in most SFF techniques, structures are formed in a layer by layer manner by solidifying or curing successive layers of a build material. For example, in stereolithography a tightly focused beam of energy, typically in the ultraviolet radiation band, is scanned across a layer of a liquid photopolymer resin to selectively cure the resin to form a structure. In Selective Deposition Modeling, herein referred to as “SDM” a phase change build material is jetted or dropped in discrete droplets, or extruded through a nozzle, to solidify on contact with a build platform or previous layer of solidified material in order to build up a three-dimensional object in a layerwise fashion. Other synonymous names for SDM used in this new industry are: solid object imaging, solid object modeling, deposition modeling, multi-jet modeling, three-dimensional printing, thermal stereolithography, and the like. Often, a thermoplastic material having a low-melting point is used as the solid modeling material, which is delivered through a jetting system such as an extruder or print head. One type of SDM process which extrudes a thermoplastic material is described in, for example, U.S. Pat. No. 5,866,058 to Batchelder et al. One type of SDM process utilizing ink jet print heads is described in, for example, U.S. Pat. No. 5,555,176 to Menhennett et al. Some thermoplastic build materials used in SDM are available and sold under the names Thermojet®2000 and Thermojet®88 by 3D Systems, Inc. of Valencia, Calif. Also, some formulations for thermoplastic phase change build materials are disclosed in U.S. Pat. No. 6,132,665 to Bui et al.
Recently, there has developed an interest in utilizing curable phase change materials in SDM. One of the first suggestions of using a radiation curable build material in SDM is found in U.S. Pat. No. 5,136,515 to Helinski, wherein it is proposed to selectively dispense a UV curable build material in a SDM system. Some of the first UV curable material formulations proposed for use in SDM systems are found in Appendix A of International Patent Publication No. WO 97/11837, where three reactive material compositions are provided. More recent teachings of using curable materials in three-dimensional printing is provided in U.S. Pat. No. 6,259,962 to Gothait and in International Publication No. WO 01/26023.
However, one of the most fundamental problems associated with SDM processes is the adverse effects resulting from gravitational forces that undesirably act on a part during the build process. All SDM processes must deal with gravitational forces. For example, most downward facing surfaces built by SDM processes need special supports in order to stabilize the part during the build process.
One method of supporting the three-dimensional object to counter the gravity problem is to utilize dissimilar materials in the build process. For example, two different solidifying materials can be selectively deposited in a layer by layer process, one material for building the part, and the other material for building the support structure. There are generally four recognized methods for removing dissimilar support material for an SDM object. Three of the methods were initially proposed in U.S. Pat. No. 5,136,515 to Helinski. The first three methods are 1) removing the support material by physical force, 2) removing the support material by application of heat, 3) removing the support material by chemical means. The forth method, having little applicability to SDM techniques, involves utilizing a powder as a support material that does not adhere to the object.
In the first separation approach, the materials are carefully selected to order to establish a weak bond joint at their juncture such that the application of an applied force separates the support structure from the part along the joint. For example, this approach is described in U.S. Pat. No. 5,617,911 to Sterett et al and in International Publication WO 01/26023 of Objet Geometries Ltd., in Rehovot, Israel. Undesirably, the application of applied force to crack or crumble away the support material from the object has limitations. For instance it is difficult, and sometimes impossible, to remove the support material for certain geometric configurations, such as in deep cavities or pockets. Further, delicate features of the three-dimensional object can be broken or damaged during the removal process.
The second separation approach is to select a support material having a lower melting point than the material of the formed object. After forming the object and support structure, the temperature of the composite is raised in order to melt out the support structure. This type of approach is described in, for example, U.S. Pat. No. 5,141,680 to Almquist et al.
The third approach is to select a support material that is soluble in a solvent in which the build material is not. After forming the object and support structure the two are submersed into the solvent in order to dissolve away the support. One problem with this approach is that as the solvent starts to saturate with removed support material, and eventually new solvent is needed. The disposal of the used solvent can be problematic. In addition, evaporative issues can arise resulting in the production of odors, and the like, when working with solvents. Thus, implementing this approach may not be user friendly or cost effective.
In the fourth approach a removable support material is deposited in particulate form, such as a powder, that is energized so as to fuse to form the part, with the unfused powder acting as the support structure. This type of approach is described in, for example, U.S. Patent No. 5,252,264 to Forderhase et al. Undesirably, however, this approach is limited for use with sintered powder materials and is generally unsuitable in applications utilizing flowable solid modeling materials to build parts.
According to the present invention, a preferred build material is an acrylate/wax based curable phase change material, and a preferred support material is a wax based non-curable phase change material. It was initially envisioned to remove the support material by application of heat whereby the support material would melt away. However, initial post processing tests utilizing heat to remove the support material undesirably effected the three-dimensional object. The thermal processing apparently caused the otherwise transparent acrylate in the object to become clouded and opaque. Further, the discoloration was not uniform throughout the object.
Thus, there is a need to develop a method and apparatus capable of removing a phase change support material dispensed to support a three-dimensional object formed from a curable phase change build material without undesirably effecting the three-dimensional object. These and other difficulties of the prior art have been overcome according to the present invention.